A hydrodynamic bearing system essentially includes a bearing sleeve, a shaft accommodated in an inner cylindrical bore of the bearing sleeve and at least one radial bearing section provided between the bearing sleeve and the shaft with the aid of which the shaft and the bearing sleeve are supported rotatably with respect to each other. A bearing gap is formed between the shaft and the bearing sleeve. The bearing gap is filled with a liquid lubricant, preferably bearing oil.
To take on axial loads, the bearing system is also provided with a hydrodynamic thrust bearing. The hydrodynamic thrust bearing is formed by a thrust plate preferably arranged at one end of the shaft and a corresponding cover plate. The cover plate forms a counter bearing to the thrust plate and seals the entire bearing system from below so that no lubricant can escape from the bearing system.
In many cases, the connection between the thrust plate and the shaft is realized by means of a press connection. With motors and hard disk drives becoming ever smaller in size, the overall length available for the bearing system is also being reduced. One method which attempts to overcome this situation involves reducing the thickness of the thrust plate. To achieve an optimal press connection, the so-called guiding ratio, the quotient of the compression length t and bore diameter d, should be greater than or equal to 1. The thinner the thrust plate, the harder it is to achieve the required perpendicularity and the greater the required excess size of the shaft in relation to the bore in order to achieve the specified press-out force. This increases the risk that on being mounted onto the shaft, the thrust plate adheres to the shaft due to local cold welding resulting in destroying the perpendicularity between the shaft and the thrust plate.
To avoid this problem when using very thin thrust plates, it is known to connect the thrust plate to the shaft by means of welding. This bonding method is disclosed in JP2000-324753. There is, however, the disadvantage and risk that the bearing system could became contaminated through welding residue that could cause damage to the bearing system. Due to the heat released during the welding process, there is an added risk that the thrust plate could be deformed and thus rendered unusable.
Another possibility revealed in U.S. Pat. No. 5,357,163 is to screw the thrust plate to the end face of the shaft. However, on one hand this means that a planar end face has to be provided at a right angle to the shaft end on the other hand this method requires an additional, fault-prone assembly effort.
Another possible solution is to form the thrust plate and the shaft as one piece. Manufacturing such an integral component with the required tolerances, however, involves a very complex and expensive process.